Slide #170
(Artery, vein, and nerve) There are several features that
allow one to distinguish between arteries and veins. Arteries
have a thicker more regular tunica media. In histological preparations
they more often retain their round profiles when cut in cross
section. Veins tend often to look "collapsed" or flattened
under the same circumstances. In addition, the tunica media of
veins is much thinner than in arteries, and the adventitia is
the thickest layer.

Identify the three layers of both arteries and veins
and note the differences in thickness.

Slide #174 In very large vessels, the adventitial
layer (outer layer) will contain blood vessels (vasa vasorum)
that supply the vessel wall. Autonomic nerves are found in all
vessels but are not evident without special staining techniques.
(i.e. don't look for nerves!)

Slide #90 (Elastic artery) This is a section of just
part of a human aorta. Notice the large constituent of elastic
fibers in the tunica media (middle layer) as compared
to the muscular artery on the previous slide. Which side of the
section is the luminal side? [hint: identifytunicaintima (inner layer)]

Various texts call vessels arterioles if the have two, three,
or up to seven layers of smooth muscle. This vessel has aboout
five layers of smooth muscle so would be an arteriole in one
text and a small muscular artery in another.

We will call any small artery with up to five layers of
smooth muscle an arteriole.

Slide #15 Human blood smear, Wright stain. While scanning
the smear, it becomes obvious that erythrocytes are the most
numerous type of cell in peripheral blood. Based on morphological
criteria, use the high-dry objective to differentiate the following
blood cells (then, if you'd like, take a closer look with your
oil immersion lense):

Erythrocytes(RBCs)- 7 to 9 u
diameter, no nucleus, rounded.
The peripheral zone of erythrocytes stains deep orange-red whereas
the central zone appears pale and at times, colorless. The size
of the central zone and the overall staining intensity of the
erythrocyte is proportional to the content of hemoglobin.

Platelets - 1 to 3 u diameter.
Platelets are cytoplasmic fragments derived from megakaryocytes.
They usually stain light blue and contain red or purple granules.
These fragments tend to form small aggregates randomly dispersed
throughout the blood smear.

I. GranulocytesAll cells in this category contain secondary (specific) granules.
The staining characteristics of secondary granules are very specific
for each cell type, thereby facilitating identification of the
three different types of granulocytes. Another distinguishing
feature is the presence of a multi-lobed nucleus. There are three
types of granulocytes.

Neutrophils (polymorphonuclear leukocytes; PMNs)--
10 to 15 u diameter.
These cells constitute 70% of leukocytes and usually have 2 to
5 nuclear lobes connected by fine filaments of chromatin. Neutrophils
are the most numerous of all leukocytes, therefore, easiest to
identify. The cytoplasm is pink to grey because of the neutral
staining of specific granules (i.e. they don't stain). Neutrophils
function as scavengers within extravascular tissue, destroying
bacteria or other infectious organisms that invade the body.
Neutrophils are also called Polymorphonuclear Leukocytes (PMNs)
in some laboratories even though the following two cell types
also have multi-lobed nuclei.

Eosinophils-- 10 to 15 um diameter
Eosinophils constitute 2.0 to 4.0% of leukocytes. These cells
usually contain a bilobate (two lobes) nucleus and a cytoplasm
full of brightly stained eosinophilic (orange-red) specific granules.
Eosinophils function specifically as phagocytes to destroy larvae
of parasites that have invaded tissues i.e. in trichinosis, schistosomiasis,
and appear to play a role in allergic responses. Other functions
of eosinophils include phagocytosis of antigen antibody complexes.

Basophils - 10 to 15 u diameter.
Basophils constituteapproximately 0.5 to 1.0% of leukocytes
and are therefore more difficult to find in a routine blood smear.
The nucleus consists of 2 to 3 lobes but is usually not as lobulated
as neutrophils. The cytoplasm is full of dark purple specific
granules. Basophils are also phagocytic, but function largely
like mast cells, (i.e. their granules contain histamine and heparin
which play an important role in initiation of the acute inflammatory
response).

II. Agranulocytes
As the name suggests, these leukocytes usually have no distinguishable
cytoplasmic granules.

Lymphocytes - 9 to 14 um diameter
Lymphocytes constitute 20 ­ 25% of agranulocytes and may
be small, medium or large in size. The nucleus is rounded or
oval, and usually the same size as an erythrocyte. The chromatin
is densely packed with no apparent nucleoli. When compared with
nuclei of other cells, the lymphocyte nucleus almost always appears
smudged. The cytoplasm is scanty and stains pale blue. Lymphocytes
are composed of two subpopulations: T lymphocytes & B lymphocytes,
which have distinctive functional differences. However, they
appear morphologically identical in the stained blood smears
you are using. Some lymphocytes migrate into the connective tissues
and become Plasma Cells.

Monocytes
- 12 to 20 um diameterMonocytes comprise 3 ­ 8% of agranulocytes. This large
cell has a lightly stained nucleus that often appears horseshoe
or kidney shaped. The chromatin appears lacy and nucleoli are
usually not apparent. The nucleus looks a bit like a "brain."
The abundant cytoplasm stainsnd quite often contains vacuoles
(small, clear areas). These areas help to distinguish monocytes
from large lymphocytes. Small dense granules are frequently present.
(Yes! even though they are called agranulocytes.) Monocytes migrate
into connective tissue and become Macrophages.

Blood Development

Slides #99 & 172 (Red bone marrow smear, human).
You should be able to identify the stages of the granulocytic
(myelocytic) and erythrocytic developmental series.

Granulocytes

All stages of cells in the granulocytic series, except myeloblasts,
will have some type of granule in the cytoplasm. Developing neutrophils
are the most numerous. The developing eosinophils and basophils
are less common and more difficult to locate.

Myeloblast - 16 to 20 u diameter
These cells are rarely seen and are difficult to distinguish
from proerythroblasts of the erythrocytic series. Prominent nucleoli
and scanty basophilic cytoplasm are two distinguishing features.
Do not try to identify this cell.

Promyelocyte - 15 to 25 u diameter
The outstanding features of cells in the promyelocyte stage are
(1) the large size, (2) rounded, indented nucleus and (3) numerous
azurophilic (deep blue, purple) or primary granules in the cytoplasm.
Do not try to identify this cell.

Modified drawing from your text. Note differences
in labeling for Basophilic Erythroblast, Early and

Late Metamyelocyte (Band or Stab), Normoblast,
and Reticulocyte

Myelocyte
- 15 to 30 u diameter
This is the first stage at which one can distinguish between
neutrophils, eosinophils and basophils by the presence of specific
granules in the cytoplasm. The shape of the nucleus is variable,
but is usually indented and displaced from the center. The cytoplasm
is spotted with azurophilic and specific granules. Most of the
cells from this stage are neutrophilic since neutrophils are
the most numerous type of mature granulocyte. Cells in the myelocyte
stage may also have clear halo bordering the indentation of the
nucleus representative of an extensive Golgi apparatus.

Metamyelocyte-
10 to 16 u diameter
These cells can also be of the neutrophilic, eosinophilic or
basophilic variety and are similar to cells in the myelocyte
stage except they (1) are smaller in size and (2) demonstrate
a deeply indented, kidney shaped nucleus.

Band Form ("Stab") - 10 to 15 u
Cells in this stage have a long, thinned-out nucleus with parallel
sides: i.e. it resembles a thick bar stretched across the center
of the cell, or, more often, a horseshoe. The rest of the cell
still shows other characteristics of a mature neutrophil.

Segmented
Form - (mature cell)
This is the mature form seen in the previous peripheral blood
slide. The distinguishing feature is the presence of several
nuclear lobes connected by thin filamentous strands of chromatin.

Erythrocytic Series

The distinguishing characteristics of cells in this series
are the lack of cytoplasmic granules and, except for the
first and last stages, a centrally placed, well rounded nucleus..Again,
just identify the underlined cells.

Proerythroblast ­ Do not try to identify this cell.

Basophilic
erythroblast - 12 to 18 u diameter
The most outstanding feature of cells in this stage is the deeply
basophilic cytoplasm. The nucleus is round with clumped chromatin
and is centrally located. These cells may be hard to distinguish
in some of your slides.

Polychromatophilic erythroblast - 10 to 12 u
diameter
These cells are smaller and the nuclear material is more condensed
than in the previous stage. Due to increased synthesis of hemoglobin,
the cytoplasm is now staining blue-grey to grey-green. Again,
note the well-rounded shape of the nucleus.

Normoblast (orthochromatophilic erythroblast)
- 9 to 11 u diameter
Called normoblasts because the cytoplasm approaches the "normal"
staining pattern of mature erythrocytes: i.e. red-orange due
to the concentration of hemoglobin. The nucleus is much smaller
and denser (pyknotic) at the periphery of the cell ready to be
extruded.

Reticulocyte - 8 to 9 u diameter
These cells are anucleate and are indistinguishable from mature
erythrocytes by routine Wright's stain. If treated with supravital
stain, cytoplasmic ribosomes and residual reticular framework
are evident.(You cannot find these cells but should know what
they are.)

Erythrocyte - 7 to 8 u diameter
These mature, functional cells are biconcave, anucleate and eosinophilic.
They contain a small area of central pallor (pale staining in
the center).

Othercellsthatmaybeseeninredbonemarrowpreparations:

Megakaryocytes - very large cells (approximately 50
to 100 u) with a convoluted nucleus. Pieces of cytoplasm break
off from these cells and are released into the circulation as
platelets. Due to their size, these cells are most apparent when
scanning the slide at low power.

Lymphocyte andmonocyte precursors - do not
concern yourself with these cells at this time.